Lithium-ion batteries are secondary batteries with a high energy density, and their characteristics are demonstrated when used as power sources for portable devices such as notebook computers and cellular phones. There are a variety of shapes of the lithium-ion batteries. Cylindrical lithium-ion batteries adopt a structure in which a positive electrode, a negative electrode, and a separator are wound. For example, two belt-like metal foils, to which a positive electrode material and a negative electrode material are applied, are stacked with a separator interposed therebetween to form a stacked member. Then, the stacked member is wound into a swirling shape to form a wound electrode group. The wound electrode group is contained in a cylindrical battery case that serves as a battery container, an electrolyte is poured into the battery case, and the battery case is sealed to form a cylindrical lithium-ion battery.
Among the cylindrical lithium-ion batteries, 18650-type lithium-ion batteries are widespread as lithium-ion batteries for consumer use. The 18650-type lithium-ion battery is small in outer dimension with a diameter of 18 mm and a height of about 65 mm. Lithium cobalt oxide with a high capacity and a long life is mainly used as the positive active material of the 18650-type lithium-ion battery. The 18650-type lithium-ion battery has a battery capacity of about 1.0 Ah to 2.0 Ah (3.7 Wh to 7.4 Wh).
In recent years, there have been expectations not only for consumer use of the lithium-ion batteries for portable devices etc., but also for development of use of the lithium-ion batteries for large-scale power storage systems that utilize natural energy such as solar and wind power generation. The large-scale power storage systems require a power storage amount in the order of several megawatt-hours per system.
For example, Patent Document 1 (WO 2013/128677 A1) discloses a cylindrical lithium-ion battery that includes a cylindrical battery container and a wound electrode group formed by winding a stacked member of a positive electrode, a separator, and a negative electrode. The battery has a discharge capacity of 30 Ah or more. A positive active material mixture that contains a composite oxide of lithium and manganese is used for the positive electrode. A negative active material mixture that contains amorphous carbon is used for the negative electrode.